Why does light seem to occlude objects in front of it

_{Image credit: By Mallowtek (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons}

The phenomenon which the opening poster (incorrectly, in my view) described as "seems to occlude" (an occlusion is an obstruction to the passage of light) is known to photographers as "veiling glare".

The above link goes to a page on the website of a commercial solution provider for testing digital image quality. As the page notes,

Veiling glare is stray light in lenses and optical systems caused by reflections between surfaces of lens elements and the inside barrel of the lens.

and

It is a strong predictor of lens flare — image fogging (loss of shadow detail and color) as well as “ghost” images — that can degrade image quality in the presence of bright light sources in or near the field of view. It occurs in every optical system, including the human eye.

The second link goes to the Wikipedia page on lens flare, which says:

Lens flare is the light scattered in lens systems through generally unwanted image formation mechanisms, such as internal reflection and scattering from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image rays. Flare manifests itself in two ways: as visible artifacts, and as a haze across the image. The haze makes the image look "washed out" by reducing contrast and color saturation (adding light to dark image regions, and adding white to saturated regions, reducing their saturation).

(All emphases mine)

_{Image credit: By Bautsch (Own work) [CC0], via Wikimedia Commons}

[Above diagram shows a] testing setup for determining undesired influence of "backlight". Grey screen at left is imaged optically via camera lens onto image plane of image sensor (or film). Red laser-light beam, source of which is 10° outside of field of view, ideally should not be imaged on image plane but absorbed inside the camera. [Translated from German Wikipedia.]

_{Image credit: By Bautsch 14:20, 18. Jan. 2011 (CET).Bautsch at de.wikipedia [Public domain], from Wikimedia Commons}

Photographic exposure taken by digital SLR camera, exhibiting undesired influence of backlight as per testing setup above. [Translated from German Wikipedia.]

Making this post Community Wiki, as I am neither a physicist nor a photographer, and I expect amplifications to be added so as to make this a more complete Answer.

Light is a wave; if you imagine a wave front passing through a buoy or a strut/leg of a pier, the wave will first be "blocked" by it, but then eventually "spread out" on the other side and fill in the hole the buoy/leg caused.

In optics we tend to refer to effects like these that result from the wave-like nature of light under the umbrella term "diffraction".

Here is an illustration to demonstrate this phenomenon; in your mind replace the block with a pier leg/buoy an the waves with water waves, or the block with your struts and the waves with light waves.

I believe the answer is as simple as diffraction. The light diffracts a bit around the intervening object, so some light is deflected such that you perceive it as coming from a direction covered by the object. This happens all the time, but is more noticeable with a very bright light source.

EDIT: I'll attempt to estimate the magnitude of the diffraction effect. I assume the far field approximation throughout. This is a back-of-the envelope approach, so I'm liberally rounding and approximating.

Diffraction of light around a macroscopic object has some similarities to single slit diffraction with a slit larger than the wavelength being diffracted. The angular extent of the central intensity peak in single slit diffraction is approximately $2\lambda/a$ ($\lambda$ is the wavelength, $a$ is the size of the object), so roughly speaking the wave is deflected by half this angle at each edge of the slit (deflection = $\lambda/a$).

The angular size of the object is simply $a/R$ ($R$ is the distance to the object) provided that the object is far away. If the deflection angle is half the angular extent of the object, the intensity peak will totally cover the object (though not at uniform intensity!), so I'd argue that it would start to be quite noticeable if the deflection angle is 5-10% of the angular size of the object:

$.05\leq \frac{\lambda R}{a^2}$

Now I need to start guessing at the values of $\lambda$, $R$ and $a$. $\lambda$ is pretty easy, the Sun emits light with a peak wavelength of about $500\mathrm{nm}$. The width of the bars in the picture aren't too difficult either, I'd estimate $a\sim5\mathrm{cm}$. The trick part is the distance from which the picture was taken... it could be zoomed or cropped and there's nothing to give perspective... so I'll take a guess and say the photographer probably wasn't standing much closer than $100\mathrm{m}$ to the structure (getting further away will amplify the effect, so this seems like a good compromise). Putting in these values, I get:

$\frac{\lambda R}{a^2} = 0.02$

This means that about 4% of the width of the bars would be covered by diffraction effects. If the picture was taken from a bit further away (maybe 500m), then coverage is up to 20%.

Additionally, there are potentially secondary peaks in the diffraction pattern contributing; the secondary peaks are much dimmer than the primary, but the Sun is very bright and I'd guess the camera detector is saturated, so even a dimmer secondary peak could potentially still get a strong signal in the detector.

Still, unless this picture was taken from quite a distance (looks like maybe 80% coverage, so about 2km, maybe a little less if my other estimates are a little off), I don't think diffraction can entirely account for the observed effect.